A. Field of the Invention
The present invention concerns the design and operation of cotton gins. More specifically, the invention is directed towards an apparatus for separating cotton fibers from foreign matter. Even more specifically, the invention discloses an improved apparatus for utilizing high velocity air movement to separate cotton lint from foreign matter.
B. Background
Cotton that is harvested from a field consists primarily of the desired cotton fibers and cotton seed and much undesirable foreign matter, such as burrs, sticks, stems and green leaf material. After harvesting, the cotton/foreign matter material is taken to a cotton gin for processing the harvested material into bulk cotton fibers and cotton seed. A large part of a modern cotton ginning plant consists of machines and processes for separating and removing the foreign matter from the cotton fiber both prior to and following the actual separation of the cotton lint from the seed (the actual ginning). For purposes of background and completeness on cotton ginning, and specifically on the equipment used in cotton ginning plants, the reader is directed to the book "Ginning Cotton--An Entrepreneur's Story" by A. L. Vandergriff, Texas Tech University Press, 1997. This book is incorporated in its entirety herein by the above reference.
The process of extracting foreign matter from the cotton is a multi-stage process, including pre-cleaners such as extractors and cylinder cleaners. Most common extractors make use of cylinders covered with aggressive, hooked teeth. As the cylinders rotate, they engage the cotton fiber/foreign matter mix and drag it over a screening surface. The screening surfaces generally consist of rods or bars mounted laterally adjacent the extractor (toothed) cylinder. Cylinder cleaners, which are generally used after the extractors described above, primarily consist of cylinders having a number of pins protruding from the surface of the cylinder. The cotton is passed between the cylinders and a screen surface, typically inclined forty to forty-five degrees, that is configured to facilitate the falling out of the small particles of foreign material remaining in the cotton stream after treatment by the extractor. To improve the separation efficiency of the cylinder cleaners the use of heated air and deflectors have been incorporated. While the extractors and cylinder cleaners used for the mechanical separation of cotton from foreign matter are generally successful in separating the seed and the larger pieces of foreign material from the cotton lint, they are generally unable to remove small particles of foreign material.
Typically, the last stage of cleaning is to remove the many small trash particles that still remain in the lint after processing by the mechanical devices. A common device for this process is the jet lint cleaner, which utilizes a high volume of air moving at a high rate of speed to separate trash from lint. The prior art jet lint cleaner has been in use for many years and was patented in the 1950s and assigned to the Lummus Cotton Gin Company of Columbus, Ga. A drawing of the process utilized by the jet lint cleaner is set forth in FIG. 1. The lint and trash, commingled together, is conveyed by air created by the gin stand doffing mechanism through the duct identified as "A" in FIG. 1. As the commingled lint and trash approaches the open slot, shown near "C" in FIG. 1, the velocity of the air increases to 5,000 to 7,000 feet per minute due to the decrease in cross-sectional area of duct "A" as it approaches "C". A negative pressure in duct "B" results in an incoming air flow at slot "C". The commingled lint and trash meets the incoming air flow at the open slot at "C". The lint turns into the outgoing duct "B" as the trash particles, having higher density, penetrate the incoming air flow and discharge into the trash chamber by exiting out slot "C".
From the jet cleaner, the cotton lint travels to a condenser where the cotton is pressed into a thin bat to be delivered to a press. The press then "presses" the cotton into a typical 500 pound bale. Samples of the cotton are cut from the bale and sent to the classification office to determine the cotton grade. Cotton grade is determined by analyzing the cotton fiber lengths and the amount of trash remaining in the lint, among other factors.
As would be expected, additional cleaning is beneficial because it can result in a better grade of cotton. In order to obtain the necessary level of clean lint, cotton gin cleaning processes utilize one or more lint cleaners at the end of the ginning process (i.e., after the jet cleaner). The typical lint cleaner has a series of saw blades that cut through the cotton lint to remove the remaining seed and trash from the lint. Unfortunately, the saws in the lint cleaners damages the cotton and has a tendency to merely break the trash into very small particles that are even more difficult to remove. The mechanical cutting action of the lint cleaners tend to lower the grade of the cotton by shredding it into small pieces, thereby damaging the spinning value. This leaves the gin operator with the choice of leaving the small particles of trash in the lint or trying to remove it with the saws in the lint cleaners. Either way, a lower grade of cotton can result, resulting in a lower price for the ginned cotton.
Clearly, it would be beneficial to not rely on the saw action of the lint cleaners to remove the small particles of foreign matter. One way to remove these particles would be to improve the operation of the jet cleaner. Because one slot works well to remove trash particles from lint, it would appear to be desirable to add additional slot systems in series to remove even more trash from the lint. However, this has not been done in the cotton industry due to the volume of air that would be required to be handled by the cleaning system in order to have a multiple slot mechanism. The use of additional volume of air would result in too much pressure build-up and would affect the condensers, which pull air in. In order to supply the additional air that would be needed, the cotton gin would need much larger fans operated by higher horsepower motors, thereby significantly increasing the energy use and cost of the cleaning process. In addition, because the exhaust air from the condensers must be cleaned prior to be discharged to the atmosphere, additional air cleaners (such as cyclone collectors) must be utilized to be able to sufficiently clean the exhaust air in compliance with stringent EPA standards. Naturally, having an increased volume of air to clean results in higher equipment and operating costs.
As a result of the problems associated with lower grade of cotton from small particles of trash in the ginned cotton or the shredding action of the saw blades in the lint cleaners, there exists a need for an apparatus that can effectively and efficiently separate cotton from the small foreign materials that remain after pre-cleaning without harming the value of the cotton.